1. Field of the Invention
This invention relates generally to web cleaning devices for cleaning toner off an image surface, for example a photoconductive drum. It is particularly suitable for cleaning residual toner left on a photoconductive drum after an efficient transfer of a toner image, for example a transfer of toner image to a heat softened thermoplastic layer using a combination of heat and pressure.
2. Background Art
U.S. Pat. No. 4,927,727 to Rimai et al, and U.S. Pat. No. 4,968,578 to Light et al, suggest a transfer process using a combination of heat and pressure to transfer toner images to a heat softened thermoplastic layer on a receiving sheet. This process has been shown to provide efficient transfer of dry toners of extremely small size, for example, toners as small as 3.5 micron (average diameter). Transfer of as much as 99 percent of such a toner has been made under conditions in which electrostatic transfer is relatively ineffective. It provides a transfer mechanism usable in forming extremely high quality color toner images using a dry electrophotographic system.
Even though as little as 1 percent of the original toner image is left on the original image member, it must be cleaned off before that portion of the image member is re-used. This creates the demanding job of cleaning off only those toner particles most difficult to transfer in a very effective transfer system. Although the use of heat in the cleaning step in addition to its use in transfer may be effective in removing more toner, it is desirable not to subject the image member to such an additional heating step. Unfortunately, conventional heavy duty cleaning mechanisms, such as fur brush or magnetic brush cleaning, are not as efficient as the aforesaid transfer method in removing small particle toner from such an image member.
Since the introduction of plain paper desk-top copiers in the early 1960's, a disposable cleaning web has been used for light-duty image member cleaning. Typically, a cleaning web of cloth or paper is supplied on a supply spool, trained around a pressure roller and taken up on a take-up spool. The pressure roller is urged by a spring into contact with the image member to clean the image member according to the surface characteristics of the web and the amount of pressure applied by the pressure roller. The take-up roller is indexed periodically by its own separate motor, or by a substantially reduced drive between it and a main drive on the image-forming device, for example, the drive for a photoconductive drum.
U.S. Pat. No. 4,530,595 issued to Itaya et al., July 23, 1985 shows the use of an endless belt cleaning device in which a voltage is impressed between an image member and a cleaning web to create a field electrostatically transferring toner from the image member to the endless web. The endless web is cleaned at a position remote from the image member.
U.S. Pat. No. 4,862,221, issued to Tabuchi et al., Aug. 29, 1989, suggests a cleaning web having supply and take-up rolls and a pressure roller in which the web itself has an alternating concave and convex pattern arranged diagonally so that every portion of a cleaned surface is contacted by both the concave and convex part of the web.
U.S. Pat. No. 4,499,849 issued to Tomita et al., on Feb. 19, 1985 shows an endless cleaning web. A counter member having a variety of shapes performs the function of a backup for the cleaning web. Both concave and convex backup members are shown.
U.S. Pat. No. 4,853,741 to Ku, issued Aug. 1, 1989, shows a web cleaning device for cleaning the back of a photoconductive web which device includes supply and take-up rolls. The web is stretched around a film ski which also supports the photoconductive web. The web is indexed a small amount periodically during operation of the image-forming apparatus in which the photoconductive web is used.